U.S. patent number 8,492,041 [Application Number 13/262,174] was granted by the patent office on 2013-07-23 for solid oxide fuel cell.
This patent grant is currently assigned to Toto Ltd.. The grantee listed for this patent is Yoshiyuki Kawamura, Kiyotaka Nakano, Toshiharu Ooe, Tsukasa Shigezumi, Katsuhisa Tsuchiya. Invention is credited to Yoshiyuki Kawamura, Kiyotaka Nakano, Toshiharu Ooe, Tsukasa Shigezumi, Katsuhisa Tsuchiya.
United States Patent |
8,492,041 |
Shigezumi , et al. |
July 23, 2013 |
Solid oxide fuel cell
Abstract
Provides a solid oxide fuel cell with which product life can be
extended while a practical output power is maintained. The present
invention is a solid oxide fuel cell, having a fuel cell module
(2), a fuel supply device (38), an oxidant gas supply device (45),
and a controller (110) for controlling the fuel supply amount;
whereby the controller is furnished with a degradation determining
circuit (110a) for determining degradation in a fuel cell module,
and with a fuel correction circuit (110b) for correcting operating
conditions based on a degradation determination; the fuel
correction circuit can execute an increasing correction mode for
increasing the fuel supply amount supplied to the fuel cell module
so that rated output power is maintained, or can execute a
decreasing correction mode for reducing rated output voltage so
that the fuel supply amount is reduced; there is also a mode
selection device (110c) for selecting correction modes.
Inventors: |
Shigezumi; Tsukasa (Kitakyushu,
JP), Ooe; Toshiharu (Kitakyushu, JP),
Tsuchiya; Katsuhisa (Kitakyushu, JP), Nakano;
Kiyotaka (Kitakyushu, JP), Kawamura; Yoshiyuki
(Kitakyushu, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Shigezumi; Tsukasa
Ooe; Toshiharu
Tsuchiya; Katsuhisa
Nakano; Kiyotaka
Kawamura; Yoshiyuki |
Kitakyushu
Kitakyushu
Kitakyushu
Kitakyushu
Kitakyushu |
N/A
N/A
N/A
N/A
N/A |
JP
JP
JP
JP
JP |
|
|
Assignee: |
Toto Ltd. (Fukuoka,
JP)
|
Family
ID: |
42828336 |
Appl.
No.: |
13/262,174 |
Filed: |
March 31, 2010 |
PCT
Filed: |
March 31, 2010 |
PCT No.: |
PCT/JP2010/055914 |
371(c)(1),(2),(4) Date: |
September 29, 2011 |
PCT
Pub. No.: |
WO2010/114047 |
PCT
Pub. Date: |
October 07, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120021317 A1 |
Jan 26, 2012 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 31, 2009 [JP] |
|
|
2009-087231 |
|
Current U.S.
Class: |
429/430; 429/495;
429/432 |
Current CPC
Class: |
H01M
8/04559 (20130101); H01M 8/0494 (20130101); H01M
8/04753 (20130101); H01M 8/04619 (20130101); H01M
8/04589 (20130101); Y02E 60/50 (20130101); H01M
2008/1293 (20130101) |
Current International
Class: |
H01M
8/04 (20060101); H01M 8/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
19523260 |
|
Mar 1997 |
|
DE |
|
05-003041 |
|
Jan 1993 |
|
JP |
|
2003-217627 |
|
Jul 2003 |
|
JP |
|
2004-164909 |
|
Jun 2004 |
|
JP |
|
2006-244821 |
|
Sep 2006 |
|
JP |
|
2007-087756 |
|
Apr 2007 |
|
JP |
|
2008-159362 |
|
Jul 2008 |
|
JP |
|
Other References
International Search Report for International Application No.
PCT/JP2010/055914, dated Jul. 20, 2010, 2 pages. cited by applicant
.
Written Opinion of the International Searching Authority for
International Application No. PCT/JP2010/055914, dated Jul. 20,
2010, 3 pages. cited by applicant .
International Preliminary Report on Patentability for International
Application No. PCT/JP2010/055914, dated Nov. 15, 2011, 5 pages.
cited by applicant .
Extended European Search Report for European Application No.
10758818.8, dated Mar. 4, 2013, 5 pages. cited by applicant .
Extended European Search Report Replacement for European
Application No. 10758818.8, dated Mar. 14, 2013, 6 pages. cited by
applicant.
|
Primary Examiner: Maples; John S
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Claims
The invention claimed is:
1. A solid oxide fuel cell system comprising: a fuel cell module
comprising multiple fuel cell units; a fuel supply device
configured to supply fuel to the fuel cell module according to a
fuel supply function which defines a relationship between a demand
for output power from a the fuel cell module and an amount of fuel
supply to the fuel cell module for meeting the demand for output
power; an oxidation gas supply device configured to supply
oxidation gas to the fuel cell module; and a controller programed
to control the amount of fuel supply from the fuel supply device,
the controller comprising a degradation determining circuit
programed to determine degradation of the fuel cell module, and a
fuel correction circuit programed to correct the fuel supply
function to adjust the amount of fuel supply from the fuel supply
device, based on a result of determination performed by the
degradation determining circuit, wherein the fuel correction
circuit is programed to execute, when the fuel cell module is
determined to have degraded, one of (i) an increasing correction
mode in which the fuel supply function is corrected to increase the
amount of fuel supply to the fuel cell module so that a maximum
rated output power of the fuel cell module is maintained, and (ii)
a decreasing correction mode in which the fuel supply function is
corrected to decrease the maximum rated output power so that the
fuel supply amount is reduced, and the solid oxide fuel cell system
has a mode selection device which selects the increasing correction
mode or the decreasing correction mode.
2. The solid oxide fuel cell system of claim 1, wherein the mode
selection device comprises an input device manually operated to
select the increasing correction mode or the decreasing correction
mode.
3. The solid oxide fuel cell system of claim 1, further comprising
an operating state recording device which records an operation
history of the fuel cell module, wherein the mode selection device
selects the increasing correction mode or the decreasing correction
mode based on the operation history of the fuel cell module
recorded in the operating state recording device.
4. The solid oxide fuel cell system of claim 3, wherein the
operating state recording device records the operation history
which comprises a history of power outputted by the fuel cell
module, and when, during a predetermined past period, a time during
which the fuel cell module was outputting the maximum rated output
power was longer than a time during which the fuel cell module was
outputting less than the maximum rated output power, the mode
selection device selects the increasing correction mode, whereas
when, during the predetermined past period, the time during which
the fuel cell module was outputting the maximum rated output power
was shorter than the time during which it was outputting less than
the maximum rated output power, the mode selection device selects
the decreasing correction mode.
Description
This application is a 371 application of PCT/JP2010/055914 having
an international filing date of Mar. 31, 2010, which claims
priority to JP2009-087231 filed Mar. 31, 2009, the entire contents
of which are incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a solid oxide fuel cell, and more
particularly to a solid oxide fuel cell for varying output power in
response to required generation amount.
BACKGROUND ART
Solid oxide fuel cells ("SOFCs" below) operate at relatively high
temperatures, using an oxide ion conducting solid electrolyte as an
electrolyte, with electrodes placed on both sides thereof, and with
fuel gas supplied to one side thereof and oxidizer (air, oxygen, or
the like) supplied to the other side thereof.
In such SOFCs, steam or CO.sub.2 is produced by the reaction
between oxygen ions passed through the oxide ion conducting solid
electrolyte and fuel, thereby generating electrical and thermal
energy. The electrical energy is extracted from the SOFC, where it
is used for various electrical purposes. At the same time, thermal
energy is used to raise the temperature of the fuel, SOFC, oxidant,
and the like.
It is known that fuel cell units degrade with usage over long time
periods. Unexamined Patent Application 2007-87756 (Patent Document
1) sets forth a solid oxide fuel cell. It is stated that in this
fuel cell, degradation of the fuel cell units can be reduced by
adjusting the flow rate of fuel.
A fuel supply amount control device, fuel supply amount control
method, and electrical power supply system are also set forth in
Unexamined Patent Application 2003-217627 (Patent Document 2). In
this fuel supply amount control device, the amount of fuel supplied
is compensated when the electrical power extractable from a
predetermined amount of fuel supplied decreases due to degradation
of fuel cell units.
PRIOR ART REFERENCES
Patent References
Patent Document 1: Unexamined Patent Application 2007-87756 Patent
Document 2: Unexamined Patent Application 2003-217627
SUMMARY OF THE INVENTION
Problems the Invention Seeks to Resolve
However, when the fuel supply amount is compensated so that the
amount supplied to a degraded fuel cell increases, as in Unexamined
Patent Application 2003-217627, thereby maintaining the same level
of output as the initial generation output, the problem arises that
degradation of the fuel cell is promoted, and product life is
shortened. On the other hand, if a control is performed to reduce
the power extracted from the degraded fuel cell, degradation of
that fuel cell can be restrained from advancing, but since the
power extractable from the fuel cell gradually diminishes, the
period over which a practical level of power can be extracted
becomes shorter.
The present invention therefore has the object of providing a solid
oxide fuel cell capable of extending product life while maintaining
a practical power output.
Means for Resolving the Problems
To resolve the above-described problems, the present invention is a
solid oxide fuel cell having: fuel cell module furnished with
multiple fuel cell units; a fuel supply device for supplying fuel
to the fuel cell module; an oxidant gas supply device for supplying
oxidant gas to the fuel cell module; and a controller for
controlling the amount of fuel supplied from the fuel supply
device; wherein the controller is furnished with a degradation
determining circuit for determining degradation of a fuel cell
module, and a fuel correction circuit for correcting operating
conditions based on the degradation determination performed by this
degradation determining circuit; whereby when it is determined that
the fuel cell module has degraded, the fuel correction circuit is
capable of executing an increasing correction mode for increasing
the fuel supply amount supplied to the fuel cell module so that the
rated output power, which is the maximum power output from the fuel
cell module, is maintained, and a decreasing correction mode for
decreasing the rated output voltage so that the fuel supply amount
is reduced; in addition, there is a mode selection device for
selecting the increasing correction mode or the decreasing
correction mode.
In the present invention thus constituted, the controller controls
the fuel supply device and the oxidant gas supply device to supply
fuel and oxidant gas to the fuel cell module.
Also, the degradation determining circuit provided with the
controller determines degradation in the fuel cell module, and the
fuel correction circuit executes a fuel correction when it is
determined that the fuel cell module has degraded. The mode
selection device selects either the increasing correction mode or
the decreasing correction mode as the fuel correction to be
executed by the fuel correction circuit.
In the present invention thus constituted, the mode selection
device selects the increasing correction mode or the decreasing
correction mode, therefore an appropriate mode can be selected in
accordance with fuel cell usage conditions, so that product life
can be extended while a practical output power is maintained.
In the present invention the mode selection device is preferably a
mode selecting operating device capable of being operated to select
an increasing correction mode or a decreasing correction mode.
In the present invention thus constituted, an appropriate
correction mode can be selected in accordance with anticipated fuel
cell usage conditions, such as the point of shipment of the fuel
cell from the factory, the point at which it is determined to have
degraded, etc.
The present invention preferably has an operating state recording
device for recording fuel cell module past operating states, and
the mode selection device automatically selects the increasing
correction mode or the decreasing correction mode based on the fuel
cell module's past operating states recorded in the operating state
recording device.
In the present invention thus constituted, the mode selection
device selects the correction mode based on past operating states,
therefore an appropriate correction mode can be automatically
selected.
In the present invention the operating state recording device
preferably records past history relating to fuel cell module output
power as past operating states of the fuel cell module, and when,
during a predetermined past period, the time during which the fuel
cell module was outputting the rated output power was longer than
the time during which it was outputting less than the rated output
power, the mode selection device selects the increasing correction
mode, whereas when, during a predetermined past period, the time
during which the fuel cell module was outputting the rated output
power was shorter than the time during which it was outputting less
than the rated output power, the mode selection device selects the
decreasing correction mode.
In the present invention thus constituted, if in the past operating
states of the fuel cell module the time during which rated output
power was being output was longer, the increasing correction mode
is selected and the rated output voltage is maintained even after
the fuel cell module degrades, therefore grid power usage charges
can be saved. On the other hand, if the rated output power output
time was shorter, the decreasing correction mode is selected, and
rated output voltage declines, therefore the amount of fuel
consumption by the fuel cell module, whose efficiency has declined
due to degradation, can be restrained and energy can be
conserved.
The present invention is a solid oxide fuel cell having: fuel cell
module furnished with multiple fuel cell units; a fuel supply means
for supplying fuel to the fuel cell module; an oxidant gas supply
means for supplying oxidant gas to the fuel cell module; and a
control means for controlling the amount of fuel supplied from the
fuel supply means; wherein the control means is furnished with a
degradation determining means for determining degradation of a fuel
cell module, and a fuel correction means for correcting operating
conditions based on the degradation determination performed by this
degradation determining means; whereby when it is determined for
the first time that the fuel cell module has degraded, the fuel
correction means is capable of executing an increasing correction
mode for increasing the fuel supply amount supplied to the fuel
cell module so that rated output power, which is the maximum power
output from the fuel cell module, is maintained, and a decreasing
correction mode for decreasing the rated power voltage so that the
fuel supply amount is reduced; in addition, there is a mode
selection means for selecting the increasing correction mode or the
decreasing correction mode.
Effect of the Invention
Using the solid oxide fuel cell of the present invention, product
life can be extended while maintaining practical output power.
BRIEF DESCRIPTION OF FIGURES
FIG. 1: An overall schematic showing a solid oxide fuel cell (SOFC)
according to an embodiment of the present invention.
FIG. 2: A front elevation sectional diagram showing a solid oxide
fuel cell (SOFC) fuel cell module according to an embodiment of the
present invention.
FIG. 3: A sectional diagram along line in FIG. 2.
FIG. 4: A partial section showing a solid oxide fuel cell (SOFC)
fuel cell unit according to an embodiment of the present
invention.
FIG. 5: A perspective diagram showing a solid oxide fuel cell
(SOFC) fuel cell stack according to an embodiment of the present
invention.
FIG. 6: A block diagram showing a solid oxide fuel cell (SOFC)
according to an embodiment of the present invention.
FIG. 7: A timing chart showing the operation at the time of startup
of a solid oxide fuel cell (SOFC) according to an embodiment of the
present invention.
FIG. 8: A timing chart showing the operation at the time of
shutdown of a solid oxide fuel cell (SOFC) according to an
embodiment of the present invention.
FIG. 9: A timing chart explaining the determination of degradation
in a solid oxide fuel cell (SOFC) according to an embodiment of the
present invention.
FIG. 10: A graph showing an example of the relationship between the
required generation amount input to the control section and the
fuel supply amount required to produce the required generation
amount.
FIG. 11: A graph showing an example of the change over time in fuel
supply amount relative to the change in required generation
amount.
FIG. 12: A flow chart showing a degradation determination procedure
using a degradation determining circuit.
FIG. 13: A timing chart schematically depicting the operating
history of a solid oxide fuel cell over approximately 1 year.
FIG. 14: A timing chart schematically depicting the operating
history of a solid oxide fuel cell over approximately 1 year.
FIG. 15: A timing chart showing an example of the action of a solid
oxide fuel cell when the decreasing correction mode is selected by
a mode selection device.
FIG. 16: A flow chart of fuel correction processing in the
decreasing correction mode.
FIG. 17: A timing chart showing an example of the action of a solid
oxide fuel cell when the increasing correction mode is selected by
a mode selection device.
FIG. 18: A flow chart of fuel correction processing in the
increasing correction mode.
FIG. 19: A flow chart showing correction mode selection by the mode
selection device in a variation.
EMBODIMENTS OF THE INVENTION
Next, referring to the attached drawings, we discuss a solid oxide
fuel cell (SOFC) according to an embodiment of the present
invention.
FIG. 1 is an overview diagram showing a solid oxide fuel cell
(SOFC) according to an embodiment of the present invention.
As shown in FIG. 1, the solid oxide fuel cell (SOFC) of this
embodiment of the present invention is furnished with a fuel cell
module 2 and an auxiliary unit 4.
The fuel cell module 2 is furnished with a housing 6; a sealed
space 8 is formed within the housing 6, mediated by insulating
material (not shown; the insulating material is not an
indispensable structure and may be omitted). Note that it is
acceptable not to provide insulating material. A fuel cell assembly
12 for carrying out the electrical generating reaction between fuel
gas and oxidant (air) is disposed in the generating chamber 10 at
the lower portion of this sealed space 8. This fuel cell assembly
12 is furnished with ten fuel cell stacks 14 (see FIG. 5), and a
fuel cell stack 14 comprises 16 fuel cell units 16 (see FIG. 4).
Thus, the fuel cell assembly 12 has 160 fuel cell units 16, all of
which are serially connected.
A combustion chamber 18 is formed above the aforementioned
generating chamber 10 in the fuel cell module 2 sealed space 8;
residual fuel gas and residual oxidizer (air) not used in the
electrical generation reaction are burned in this combustion
chamber 18 and produce exhaust gas.
A reformer 20 for reforming fuel gas is disposed at the top of the
combustion chamber 18; the reformer 20 is heated by the heat of
residual gas combustion to a temperature at which the reforming
reaction can take place. An air heat exchanger 22 for receiving
combustion heat and heating the air is further disposed above this
reformer 20.
Next, the auxiliary unit 4 is furnished with a pure water tank 26
for holding water from a municipal or other water supply source 24
and filtering it into pure water, and a water flow rate regulator
unit 28 (a "water pump" or the like driven by a motor) for
regulating the flow rate of water supplied from the reservoir tank.
The auxiliary tank 4 is further furnished with a gas shutoff valve
32 for shutting off the fuel gas supply from a fuel supply source
30 such as municipal gas or the like, and a fuel flow rate
regulator unit 38 (a "fuel pump" or the like driven by a motor) for
regulating the flow rate of fuel gas. Furthermore, an auxiliary
unit 4 is furnished with an electromagnetic valve 42 for shutting
off air serving as an oxidizer supplied from an air supply source
40, a reforming air flow rate regulator unit 44 and generating air
flow rate regulator unit 45 ("air blower" or the like driven by a
motor) for regulating air flow rate, a first heater 46 for heating
reforming air supplied to the reformer 20, and a second heater 48
for heating generating air supplied to the generating chamber. This
first heater 46 and second heater 48 are provided in order to
efficiently raise the temperature at startup, and may be
omitted.
Next, a hot-water producing device 50 supplied with exhaust gas is
connected to the fuel cell module 2. Municipal water from a water
supply source 24 is supplied to this hot-water producing device 50;
this water is turned into hot water by the heat of the exhaust gas,
and is supplied to a hot water reservoir tank in an external water
heater, not shown.
A control box 52 for controlling the amount of fuel gas supplied,
etc. is connected to the fuel cell module 2.
Furthermore, an inverter 54 serving as an electrical power
extraction unit (electrical power conversion unit) for supplying
electrical power generated by the fuel cell module to the outside
is connected to the fuel cell module 2.
The internal structure of the solid oxide fuel cell (SOFC) fuel
cell module of this embodiment of the present invention is
explained using FIGS. 2 and 3. FIG. 2 is a side elevation sectional
diagram showing a fuel cell module in a solid oxide fuel cell
(SOFC) according to an embodiment of the present invention; FIG. 3
is a sectional diagram along line of FIG. 2.
As shown in FIGS. 2 and 3, starting from the bottom in the sealed
space 8 within the fuel cell module 2 housing 6, a fuel cell
assembly 12, a reformer 20, and an air heat exchanger 22 are
arranged in sequence, as described above.
A pure water guide pipe 60 for introducing pure water on the
upstream end of the reformer 20, and a reform gas guide pipe 62 for
introducing the fuel gas and reforming air to be reformed, are
attached to the reformer 20; a vaporizing section 20a and a
reforming section 20b are formed in sequence starting from the
upstream side within the reformer 20, and the reforming section 20b
is filled with a reforming catalyst. Fuel gas and air blended with
the steam (pure water) introduced into the reformer 20 is reformed
by the reforming catalyst used to fill in the reformer 20.
Appropriate reforming catalysts are used, such as those in which
nickel is imparted to the surface of aluminum spheres, or ruthenium
is imparted to aluminum spheres.
A fuel gas supply line 64 is connected to the downstream end of the
reformer 20; this fuel gas supply line 64 extends downward, then
further extends horizontally within a manifold 66 formed under the
fuel cell assembly 12. Multiple fuel supply holes 64b are formed on
the bottom surface of a horizontal portion 64a of the fuel gas
supply line 64; reformed fuel gas is supplied into the manifold 66
from these fuel supply holes 64b.
A lower support plate 68 provided with through holes for supporting
the above-described fuel cell stack 14 is attached at the top of
the manifold 66, and fuel gas in the manifold 66 is supplied into
the fuel cell unit 16.
Next, an air heat exchanger 22 is provided over the reformer 20.
This air heat exchanger 22 is furnished with an air concentration
chamber 70 on the upstream side and two air distribution chambers
72 on the downstream side; these air concentration chamber 70 and
the distribution chambers 72 are connected using six air flow
conduits 74. Here, as shown in FIG. 3, three air flow conduits 74
form a set (74a, 74b, 74c, 74d, 74e, 74f); air in the air
concentration chamber 70 flows from each set of the air flow
conduits 74 to the respective air distribution chambers 72.
Air flowing in the six air flow conduits 74 of the air heat
exchanger 22 is pre-heated by rising combustion exhaust gas from
the combustion chamber 18.
Air guide pipes 76 are connected to each of the respective air
distribution chambers 72; these air guide pipes 76 extend downward,
communicating at the bottom end side with the lower space in the
generating chamber 10, and introducing preheated air into the
generating chamber 10.
Next, an exhaust gas chamber 78 is formed below the manifold 66. As
shown in FIG. 3, an exhaust gas conduit 80 extending in the
vertical direction is formed on the insides of the front surface 6a
and the rear surface 6b which form the faces in the longitudinal
direction of the housing 6; the top end side of the exhaust gas
conduit 80 communicates with the space in which the air heat
exchanger 22 is disposed, and the bottom end side communicates with
the exhaust gas chamber 78. An exhaust gas discharge pipe 82 is
connected at approximately the center of the bottom surface of the
exhaust gas chamber 78; the downstream end of this exhaust gas
discharge pipe 82 is connected to the above-described hot water
producing device 50 shown in FIG. 1.
As shown in FIG. 2, an ignition device 83 for starting the
combustion of fuel gas and air is disposed on the combustion
chamber 18.
Next we discuss the fuel cell unit 16, referring to FIG. 4. FIG. 4
is a partial section showing a solid oxide fuel cell (SOFC) fuel
cell unit according to an embodiment of the present invention.
As shown in FIG. 4, the fuel cell unit 16 is furnished with a fuel
cell 84 and internal electrode terminals 86, respectively connected
to the respective terminals at the top and bottom of the fuel cell
84.
The fuel cell 84 is a tubular structure extending in the vertical
direction, furnished with a cylindrical internal electrode layer
90, on the inside of which is formed a fuel gas flow path 88, a
cylindrical external electrode layer 92, and an electrolyte layer
94 between the internal electrode layer 90 and the external
electrode layer 92. This internal electrode layer 90 is a fuel
electrode through which fuel gas passes, and is a (-) pole, while
the external electrode layer 92 is an air electrode which contacts
the air, and is a (+) pole.
The internal electrode terminals 86 attached at the top end and
bottom ends of the fuel cell device 16 have the same structure,
therefore we will here discuss specifically the internal electrode
terminal 86 attached at the top end side. The top portion 90a of
the inside electrode layer 90 is furnished with an outside
perimeter surface 90b and top end surface 90c, exposed to the
electrolyte layer 94 and the outside electrode layer 92. The inside
electrode terminal 86 is connected to the outer perimeter surface
90b of the inside electrode layer 90 through a conductive seal
material 96, and is electrically connected to the inside electrode
layer 90 by making direct contact with the top end surface 90c of
the inside electrode layer 90. A fuel gas flow path 98
communicating with the inside electrode layer 90 fuel gas flow path
88 is formed at the center portion of the inside electrode terminal
86.
The inside electrode layer 90 is formed, for example, from at least
one of a mixture of Ni and zirconia doped with at least one type of
rare earth element selected from Ca, Y, Sc, or the like; or a
mixture of Ni and ceria doped with at least one type of rare earth
element; or any mixture of Ni with lanthanum gallate doped with at
least one element selected from among Sr, Mg, Co, Fe, or Cu.
The electrolyte layer 94 is formed, for example, from at least one
of the following: zirconia doped with at least one type of rare
earth element selected from among Y, Sc, or the like; ceria doped
with at least one type of selected rare earth element; or lanthanum
gallate doped with at least one element selected from among Sr or
Mg
The outside electrode layer 92 is formed, for example, from at
least one of the following: lanthanum manganite doped with at least
one element selected from among Sr or Ca; lanthanum ferrite doped
with at least one element selected from among Sr, Co, Ni, or Cu;
lanthanum cobaltite doped with at least one element selected from
among Sr, Fe, Ni, or Cu; silver, or the like.
Next we discuss the fuel cell stack 14, referring to FIG. 5. FIG. 5
is a perspective view showing the fuel cell stack in a solid oxide
fuel cell (SOFC) according to an embodiment of the present
invention.
As shown in FIG. 5, the fuel cell stack 14 is furnished with
sixteen fuel cell units 16; the top end side and bottom end side of
these fuel cell units 16 are respectively supported by a lower
support plate 68 and upper support plate 100. Through holes 68a and
100a, through which the inside electrode terminal 86 can penetrate,
are provided on this lower support plate 68 and outer support plate
100.
In addition, a current collector 102 and an external terminal 104
are attached to the fuel cell unit 16. This current collector 102
is integrally formed by a fuel electrode connecting portion 102a,
which is electrically connected to the inside electrode terminal 86
attached to the inside electrode layer 90 serving as the fuel
electrode, and by an air electrode connecting portion 102b, which
is electrically connected to the entire external perimeter surface
of the outside electrode layer 92 serving as the air electrode. The
air electrode connecting portion 102b is formed of a vertical
portion 102c extending vertically along the surface of the outside
electrode layer 92, and multiple horizontal portions 102d extending
in the horizontal direction from this vertical portion 102c along
the surface of the outside electrode layer 92. The fuel electrode
connecting portion 102a extends linearly in an upward or downward
diagonal direction from the vertical portion 102c of the air
electrode connecting portion 102b toward the inside electrode
terminals 86 positioned in the upper and lower directions on the
fuel cell unit 16.
Furthermore, electrode terminals 86 at the top and bottom ends of
the two fuel cell units 16 positioned at the end of the fuel cell
stack 14 (at the front and back sides on the left edge in FIG. 5)
are respectively connected to the outside terminals 104. These
external terminals 104 are connected to the external terminals 104
(not shown) at the ends of the adjacent fuel cell stack 14, and as
described above, all of the 160 fuel cell units 16 are connected in
series.
Next, referring to FIG. 6, we discuss the sensors attached to the
solid oxide fuel cell (SOFC) according to the present embodiment.
FIG. 6 is a block diagram showing a solid oxide fuel cell (SOFC)
according to an embodiment of the present invention.
As shown in FIG. 6, a solid oxide fuel cell device 1 is furnished
with a control unit 110; an operating device 112 provided with
operating buttons such as "ON" or "OFF" for user operation, a
display device 114 for displaying various data such as a generator
output value (Watts), and a notification device 116 for issuing
warnings during abnormal states and the like are connected to this
control unit 110. This notification device 116 may be connected to
a remote control center to inform the control center of abnormal
states.
Next, signals from the various sensors described below are input to
the control unit 110.
First, a flammable gas detection sensor 120 detects gas leaks and
is attached to the fuel cell module 2 and the auxiliary unit 4.
The purpose of the CO gas detection sensor 120 is to detect leakage
of CO in the exhaust gas, which is meant to be exhausted to the
outside via the exhaust gas conduit 80, into the external housing
(not shown) which covers the fuel cell module 2 and the auxiliary
unit 4.
A water reservoir state detection sensor 124 detects the
temperature and amount of hot water in a water heater (not
shown).
An electrical power state detection sensor 126 detects current,
voltage, and the like in the inverter 54 and in a distribution
panel (not shown).
A generator air flow rate detection sensor 128 detects the flow
rate of generator air supplied to the generating chamber 10.
A reforming air flow rate sensor 130 detects the rate of reforming
air flow supplied to the reformer 20.
A fuel flow rate sensor 132 detects the flow rate of fuel gas
supplied to the reformer 20.
A water flow rate sensor 134 detects the flow rate of pure water
(steam) supplied to the reformer 20.
A water level sensor 136 detects the water level in pure water tank
26.
A pressure sensor 138 detects pressure on the upstream side outside
the reformer 20
An exhaust temperature sensor 140 detects the temperature of
exhaust gas flowing into the hot water producing device 50.
As shown in FIG. 3, a generating chamber temperature sensor 142 is
disposed on the front surface side and rear surface side around the
fuel cell assembly 12, and detects the temperature around the fuel
cell stack 14 in order to estimate the temperature of the fuel cell
stack 14 (i.e., of the fuel cell 84 itself).
A combustion chamber temperature sensor 144 detects the temperature
in combustion chamber 18.
An exhaust gas chamber temperature sensor 146 detects the
temperature of exhaust gases in the exhaust gas chamber 78.
A reformer temperature sensor 148 detects the temperature of the
reformer 20 and calculates the reformer 20 temperature from the
intake and exit temperatures on the reformer 20.
If the solid oxide fuel cell (SOFC) is placed outdoors, the outside
temperature sensor 150 detects the temperature of the outside
atmosphere. Sensors to detect outside atmospheric humidity and the
like may also be provided.
Signals from these various sensor types are sent to the control
unit 110; the control unit 110 sends control signals to the water
flow rate regulator unit 28, the fuel flow rate regulator unit 38,
the reforming air flow rate regulator unit 44, and the generating
air flow rate regulator unit 45 based on data from the sensors, and
controls the flow rates in each of these units.
The control unit 110 sends control signals to the inverter 54 to
control the amount of electrical power supply.
Next, referring to FIG. 7, we discuss the operation of a solid
oxide fuel cell (SOFC) according to the present embodiment at the
time of start up.
FIG. 7 is a timing chart showing the operations of a solid oxide
fuel cell (SOFC) according to an embodiment of the present
invention at the time of start up.
At the beginning, in order to warm up the fuel cell module 2,
operation starts in a no-load state, i.e., with the circuit which
includes the fuel cell module 2 in an open state. At this point
current does not flow in the circuit, therefore the fuel cell
module 2 does not generate electricity.
First, reforming air is supplied from the reforming air flow rate
regulator unit 44 through a first heater 46 to the reformer 20 on
the fuel cell module 2. At the same time, generating air is
supplied from the generating air flow rate regulator unit 45
through a second heater 48 to the air heat exchanger 22 of the fuel
cell module 2, and this generating air reaches the generating
chamber 10 and the combustion chamber 18.
Immediately thereafter, fuel gas is also supplied from the fuel
flow rate regulator unit 38, and fuel gas into which reform air is
blended passes through the reformer 20, the fuel cell stack 14, and
the fuel cell unit 16 to reach the combustion chamber 18.
Next, ignition is brought about by the ignition device 83, and fuel
gas and air (reforming air and generating air) supplied to the
combustion chamber 18 is combusted. This combustion of fuel gas and
air produces exhaust gas; the generating chamber 10 is warmed by
this exhaust gas, and when the exhaust gas rises in the fuel cell
module 2 sealed space 8, the fuel gas, which includes reforming air
in the reformer 20 is warmed, as is the generating air inside the
air heat exchanger 22.
At this point, fuel gas into which reform air is blended is
supplied to the reformer 20 by the fuel flow rate regulator unit 38
and the reforming air flow rate regulator unit 44, therefore the
partial oxidation reforming reaction PDX given by Expression (1)
proceeds. This partial oxidation reforming reaction PDX is an
exothermic reaction, and therefore has favorable starting
characteristics. The fuel gas whose temperature has risen is
supplied from the fuel gas supply line 64 to the bottom of the fuel
cell stack 14, and by this means the fuel cell stack 14 is heated
from the bottom, and the combustion chamber 18 is also heated by
the combustion of the fuel gas and air, so that the fuel stack 14
is also heated from above, enabling as a result an essentially
uniform rise in temperature in the vertical direction of the fuel
cell stack 14. Even though the partial oxidation reforming reaction
PDX is progressing, the ongoing combustion reaction between fuel
gas and air is continued in the combustion chamber 18.
C.sub.mH.sub.n+xO.sub.2.fwdarw.aCO.sub.2+bCO+cH.sub.2 (1)
When the reformer temperature sensor 148 detects that the reformer
20 has reached a predetermined temperature (e. g. 600.degree. C.)
after the start of the partial oxidation reforming reaction PDX, a
pre-blended gas of fuel gas, reforming air, and steam is applied to
the reformer 20 by the water flow rate regulator unit 28, the fuel
flow rate regulator unit 38, and the reforming air flow rate
regulator unit 44. At this point an auto-thermal reforming reaction
ATR, which makes use of both the aforementioned partial oxidation
reforming reaction PDX and the steam reforming reaction SR
described below, proceeds in the reformer 20. This auto-thermal
reforming reaction ATR can be internally thermally balanced,
therefore the reaction proceeds in a thermally independent fashion
inside the reformer 20. In other words, when there is a large
amount of oxygen (air), heat emission by the partial oxidation
reforming reaction PDX dominates, and when there is a large amount
of steam, the endothermic steam reforming reaction SR dominates. At
this stage, the initial stage of startup has passed and some degree
of elevated temperature has been achieved within the generating
chamber 10, therefore even if the endothermic reaction is dominant,
no major drop in temperature will be caused. Also, the combustion
reaction continues within the combustion chamber 18 even as the
auto-thermal reforming reaction ATR proceeds.
When the reformer temperature sensor 146 detects that the reformer
20 has reached a predetermined temperature (e. g., 700.degree. C.)
following the start of the auto-thermal reforming reaction ATR
shown as Expression (2), the supply of reforming air by the
reforming air flow rate regulator unit 44 is stopped, and the
supply of steam by the water flow rate regulator unit 28 is
increased. By this means, a gas containing no air and only
containing fuel gas and steam is supplied to the reformer 20, where
the steam reforming reaction SR of Expression (3) proceeds.
C.sub.mH.sub.n+xO.sub.2+yH.sub.2O.fwdarw.aCO.sub.2+bCO+cH.sub.2 (2)
C.sub.mH.sub.n+xH.sub.2O.fwdarw.aCO.sub.2+bCO+cH.sub.2 (3)
This steam reforming reaction SR is an endothermic reaction,
therefore the reaction proceeds as a thermal balance is maintained
with the combustion heat from the combustion chamber 18. At this
stage, the fuel cell module is in the final stages of startup,
therefore the temperature has risen to a sufficiently high level
within the generating chamber 10 so that no major temperature
dropped is induced in the generating chamber 10 even though an
endothermic reaction is proceeding. Also, the combustion reaction
continues to proceed in the combustion chamber 18 even as the steam
reforming reaction SR is proceeding.
Thus, after the fuel cell module 2 has been ignited by the ignition
device 83, the temperature inside the generating chamber 10
gradually rises as a result of the partial oxidation reforming
reaction PDX, the auto-thermal reforming reaction ATR, and the
steam reforming reaction SR which proceed in that sequence. Next,
when the temperature inside the generating chamber 10 and the
temperature of the fuel cell 84 reaches a predetermined generating
temperature which is lower than the rated temperature at which the
cell module 2 can be stably operated, the circuit which includes
the fuel cell module 2 is closed, electrical generation by the fuel
cell module 2 begins, and current then flows to the circuit.
Generation of electricity by the fuel cell module 2 causes the fuel
cell 84 itself to emit heat, such that the temperature of the fuel
cell 84 rises. As a result, the rated temperature at which the fuel
cell module 2 is operated becomes, for example, 600.degree.
C.-800.degree. C.
Following this, a amount of fuel gas and air greater than that
consumed by the fuel cell 84 is applied in order to maintain the
rated temperature and continue combustion inside the combustion
chamber 18. Generation of electricity by the high reform-efficiency
steam reforming reaction SR proceeds while electricity is being
generated.
Next, referring to FIG. 8, we discuss the operation upon stopping
the solid oxide fuel cell (SOFC) of the present embodiment. FIG. 8
is a timing chart showing the operations which occur upon stopping
the solid oxide fuel cell (SOFC) of the present embodiment.
As shown in FIG. 8, when stopping the operation of the fuel cell
module 2, the fuel flow rate regulator unit 38 and the water flow
rate regulator unit 28 are first operated to reduce the amount of
fuel gas and steam being supplied to the reformer 20.
When stopping the operation of the fuel cell module 2, the amount
of generating air supplied by the reforming air flow rate regulator
unit 44 into the fuel cell module 2 is being increased at the same
time that the amount of fuel gas and steam being supplied to the
reformer 20 is being reduced; the fuel cell assembly 12 and the
reformer 20 are air cooled to reduce their temperature. Thereafter,
when the temperature of the generating chamber drops to, for
example, 400.degree. C., supply of the fuel gas and steam to the
reformer 20 is stopped, and the steam reforming reaction SR in the
reformer 20 ends. Supply of the generating air continues until the
temperature in the reformer 20 reaches a predetermined temperature,
e. g. 200.degree. C.; when the predetermined temperature is
reached, the supply of generating air from the generating air flow
rate regulator unit 45 is stopped.
Thus in the present embodiment the steam reforming reaction SR by
the reformer 20 and cooling by generating air are used in
combination, therefore when the operation of the fuel cell module 2
is stopped, that operation can be stopped relatively quickly.
Next, referring to FIGS. 9 through 14, we discuss the operation of
the solid oxide fuel cell 1 according to an embodiment of the
present invention.
First, referring to FIGS. 9 through 12, we discuss the load
following operation of the solid oxide fuel cell 1 and the fuel
cell module 2 degradation determination.
FIG. 9 is a timing chart explaining the determination of
degradation in a solid oxide fuel cell (SOFC) according to an
embodiment of the present invention. FIG. 10 is graph showing an
example of the relationship between the required generation amount
input to the control section 110 and the fuel supply amount
required to produce the required generation amount. FIG. 11 is
graph showing an example of the change over time in fuel supply
amount relative to the change in required generation amount. FIG.
12 is a flow chart showing a degradation determination procedure
using a degradation determining circuit.
At times t0-t1 in FIG. 9, the solid oxide fuel cell 1 is performing
a load following operation so that an output power can be obtained
in accordance with the amount of generation required by the
inverter 54 (FIG. 6). As shown in FIG. 6, that is, the control
section 110 serving as controller sends signals to the fuel flow
rate regulator unit 38 serving as fuel supply device, the reforming
air flow regulator unit 44 serving as oxidant gas supply device,
and the water flow rate regulator unit 28 serving as water supply
device in accordance with the amount of generation required from
the inverter 54, and supplies the required flow rates of fuel, air,
and water to the fuel cell module 2. The output power of the solid
oxide fuel cell 1 thus varies, as shown in FIG. 9, so as to follow
the amount of generation required from the inverter 54. A delay is
here applied to the fuel supply amount, so output power is delayed
relative to the amount of fuel supplied, and there is virtually no
change in output power relative to sudden changes in the required
generation amount. Note that the control section 110, the fuel flow
rate regulator unit 38, the generating air flow rate regulator unit
45, and the water flow rate regulator unit 28 respectively function
as a control means, a fuel supply means, an oxidant gas supply
means, and a water supply means.
The control section 110 determines the fuel supply amount using a
graph, one example of which is shown in FIG. 10, in response to the
amount of generation required from the inverter 54 and controls the
fuel flow rate regulator unit 38 such that the determined amount
(flow rate) of fuel is supplied to the fuel cell module 2. After
the initial start of use of the solid oxide fuel cell 1 up until a
determination is made that the fuel cell module 2 has degraded, the
control section 110 determines a fuel supply amount relative to the
required generation amount in accordance with curve F0 in FIG. 10.
As shown in FIG. 10, the fuel supply amount is determined in such a
way that it grows monotonically with the increase in required
generation amount, but under a required generation amount of
approximately 200 W, the fuel supply amount is approximately a
fixed value.
When the required generation amount is changed, sudden changes in
the fuel supply amount can hasten degradation of the fuel cell
module 2, therefore the fuel supply amount is gradually increased
or decreased as shown in FIG. 11. FIG. 11 is a graph showing an
example of the change in fuel supply amount versus time when the
required generation amount is changed in a stepped manner from 500
W to 700 W. As shown in FIG. 11, when the required generation
amount is changed from 500 W to 700 W at time t10, the required
fuel supply amount is suddenly changed from a fuel supply amount
for an output power of 500 W to one corresponding to 700 W. In
response, the control section 110 controls the fuel flow rate
regulator unit 38 so that the fuel supply amount is increased
slowly, as shown by the imaginary line in FIG. 11, to avoid a
sudden increase in the fuel supply amount. Note that after the
initial start of use of the solid oxide fuel cell 1, up until a
determination is made that the fuel cell module 2 has degraded, the
control section 110 increases the fuel supply amount in accordance
with the line F10 in FIG. 11.
Similarly at time t11, even if the required generation amount
changes from 700 W to 500 W, the control section 110 gradually
decreases the fuel supply amount as shown by line F10 in FIG. 11 so
that there is not a sudden decrease in the fuel supply amount. Note
that the rate of change in the fuel supply amount is set to be more
gradual when increasing the fuel supply amount than when decreasing
it.
Note that FIGS. 10 and 11 relate to fuel supply amount, but changes
occur similarly in the air supply amount and water supply amount
relative to the required generation amount.
Next, at time t1 in FIG. 9, the degradation determining circuit
110a serving as degradation determining means built into the
control section 110 starts operation of the degradation determining
mode (FIG. 6). Note that the degradation determining circuit 110a
comprises a microprocessor, a memory, a program for activating
same, and the like (none of the above is shown). FIG. 12 is a flow
chart showing the process carried out by the degradation
determining circuit 110a.
The flow chart shown in FIG. 12 is executed at a regular
predetermined time interval by the degradation determining circuit
110a. First, in step S1, a determination is made of time elapsed
since the previous degradation determining mode operation. If the
predetermined 2 week degradation determining interval has not
elapsed since the previous degradation determining mode operation,
the system advances to step S9, and one iteration of this flow
chart is completed. This process makes it possible to prevent
wasting of fuel, etc. caused by unnecessarily frequent execution of
the degradation determining mode operation.
If the 2 week degradation determining interval or more has elapsed
since the previous degradation determining mode operation, the
system advances to step S2, and a judgment is made as to whether
the solid oxide fuel cell 1 external environment is in a
predetermined degradation determining atmosphere state appropriate
to the degradation determining mode operation. Specifically, a
determination is made as to whether the outside air temperature and
outside air humidity detected by the outside air temperature sensor
150 (FIG. 6) and outside air humidity sensor (not shown) conform to
predetermined conditions. In the present embodiment, if the outside
air temperature is 5-30.degree. C. and the outside air humidity is
30-70%, the outside environment is judged to be in a degradation
determining atmospheric state appropriate to the degradation
determining mode operation. If it is judged that the external
environment is not in a degradation determining outside atmospheric
state, the system advances to step S9, and one iteration of this
flow chart is completed.
Note that this embodiment is constituted so that the degradation
determination is performed on a biweekly cycle, but that high
frequency is a disadvantage from the standpoint of energy
conservation, since it means a forced changeover to the degradation
determining mode, described below, with no load following control.
It is therefore desirable that this be set according to the degree
of performance degradation; a frequency of once every 6 months is
desirable if degradation is small. An even more desirable format
would be to use a frequency of once a year in the initial period
when the length of time operated is still short, since there is
little degradation, then as the operating length grows to 5 years,
10 years, and so forth, to shorten the determination period length.
In the present embodiment we have adopted an extremely easy to
understand form as an example.
When the outside environment is suited to the degradation
determining mode operation, the system advances to step S3, and the
degradation determining mode operation is started.
Moreover, in step S4 certain values are fixed at predetermined
supply amounts for which fuel, air, and water supply amounts are
set in advance. In other words, in the degradation determining mode
operation, the degradation determining circuit 110a controls the
fuel flow rate regulator unit 38, the generating air flow rate
regulator unit 45, and the water flow rate regulator unit 28 so
that they maintain a fixed fuel supply amount irrespective of the
generation amount being required of the control section 110. At
time t1 in FIG. 9 of the present embodiment, the degradation
determining fuel supply amount is fixed at 3 L/min, the degradation
determining oxidant gas supply amount at 100 L/min, and the
degradation determining water supply amount at 8 mL/min.
These fixed values for the fuel, air, and water supply amounts are
supply amounts obtained in advance by experimentation as the
amounts with which 700 W, which is the rated generation amount of
the solid oxide fuel cell 1 of the present embodiment, can be
generated. Therefore although there are individual differences
between fuel cells, the solid oxide fuel cell 1 has the ability to
output 700 W during the time when fuel, air, and water are supplied
at these fixed values. However, if the power extracted from the
fuel cell module 2 changes in response to the required generation
amount, then even if the fuel supply amount etc. are fixed, the
operating state of the fuel cell module 2 will not be sufficiently
stable. For this reason, in the present embodiment power is not
extracted from the fuel cell module 2 during the degradation
determining mode operation, regardless of the required generation
amount (i.e., fuel corresponding to the rated generation amount is
supplied, but the power actually generated is 0). Therefore while
the degradation determining mode operation is ongoing, supplied
fuel is not used for generation, but is combusted in the combustion
chamber 18.
Note that in the present embodiment the fixed values for fuel
supply and the like are set at values corresponding to rated
generation amount, but these fixed values can be set as desired.
The fuel cell module 2 is preferably capable of being thermally
autonomous, and can be set at a value permitting generation of
power at close to the rated generation amount, with temperature
varying sufficiently greatly according to the degree of degradation
of the fuel cell module 2. In the present embodiment power is not
extracted from the fuel cell module 2 during the degradation
determining mode operation, but it is possible to constitute the
solid oxide fuel cell 1 so that a fixed power is extracted during
the degradation determining mode operation, thereby performing the
degradation determination with the fuel cell module 2 in a
stabilized operating state. In an environment in which power can be
generated and sold using the solid oxide fuel cell 1, an operating
state in which fixed power is extracted can be easily obtained. It
is also acceptable to furnish the solid oxide fuel cell 1 with a
dummy load such as a heater (not shown) for consuming power
produced during the degradation determining mode operation, so that
a fixed power is extracted by causing the power produced to be thus
consumed.
Next, in step S5 of FIG. 12, after operation using fixed values has
begun, a judgment is made as to whether sufficient time has elapsed
and a stable operating state has been achieved. In the present
invention, the operating state stabilizes when the degradation
determining time of 5 hours has elapsed after starting operation
according to fixed values, and a judgment is made that the
predetermined degradation determining operating conditions have
been satisfied. If the fixed value-based time of 5 hours after
start of operation has not elapsed, the step S5 process is
repeated. Operation using fixed values started in step S4 is thus
maintained over a period of 5 hours (FIG. 9, times t1-t2).
After fixed value-based operation has continued for 5 hours, the
system advances to step S6 at time t2 in FIG. 9, and a judgment is
made as to whether the temperature of the fuel cell unit 16
measured by the generating chamber temperature sensor 142 is equal
to or greater than a predetermined temperature. In other words,
degradation of the fuel cell module 2 is determined by comparing
the temperature of the fuel cell module 2 resulting from operating
the fuel cell module 2 in a stable operating state with a reference
temperature serving as a predetermined degradation determination
reference temperature (the ideal stack temperature value produced
in the rated 700 W stable operating state with no degradation of
the fuel cell module 2). In the solid oxide fuel cell 1 of the
present embodiment, the reference temperature T0 of the fuel cell
module 2 when operated at rated power of 700 W in the initial state
is approximately 700.degree. C.; as degradation of the fuel cell
module 2 progresses, this temperature rises. This is caused by
degradation of the fuel cell units 16 themselves, which are solid
oxide fuel cells, and by joule heating and the like due to
increased internal resistance of the fuel cell stack 14 as the
result of degradation in the junction portion which electrically
connects the various fuel cell units 16.
In the present embodiment, the degradation determining circuit 110a
determines that the fuel cell module 2 has degraded when the
temperature T1 measured by the generating chamber temperature
sensor 142 is 30.degree. C. or more above the reference temperature
T0. If the fuel cell module 2 has not degraded, the system advances
to step S10, and one iteration of this flow chart process is
completed; no change is made to operating conditions such as the
fuel supply amount.
If it is determined that a fuel cell module 2 has degraded, the
system advances to step S7, and degradation processing is started.
In step S7 a fuel supply correction is executed by the fuel
correction circuit 110b (FIG. 6), which is a fuel correction means
built into the control section 110, and the fuel supply amount and
fuel supply amount gain relative to the required generation amount
are changed. In other words, when it is determined for the first
time after the start of use of the solid oxide fuel cell 1 that the
fuel cell module 2 has degraded, the fuel correction circuit 110b
changes the fuel supply amount relative to the required generation
amount using the fuel supply correction from the curve F0 to the
curve F1 or the curve F-1 in FIG. 10, and thereafter determines the
fuel supply amount using the curves F1 or F-1. The rate of change
when changing the fuel supply amount is changed from line F10 to
more gradual line F11 in FIG. 11, and thereafter the fuel supply
amount is changed using this rate of change. The fuel supply amount
changed by the fuel supply correction is maintained until it is
determined that the fuel cell module 2 has further degraded.
Note the selection of whether to perform the fuel supply correction
in the increasing correction mode using the curve F1 or in the
decreasing correction mode using the curve F-1 is made, as
explained below, by the mode selection device 110c serving as mode
selection means and the operating state recording device 110d
serving as operating state recording means, both built into the
control section 110. The fuel correction circuit 110b, mode
selection device 110c, and operating state recording device 110d
comprise a microprocessor, memory, a program for activating same,
and the like (none of the above is shown).
In step S7, after a correction to the fuel supply amount is carried
out, the system advances to step S8; in step S8 the temperature T2
of the fuel cell units 16 when the solid oxide fuel cell 1 is
operated using the post-correction fuel supply amount is measured
by the generating chamber temperature sensor 142. The measured
temperature T2 is stored in the degradation determining circuit
110a memory (not shown) as a new reference temperature T0. This new
reference temperature T0 is used as the reference temperature for
the next degradation determination. The temperature T2 of the fuel
cell units 16 is preferably measured after operation is conducted
with the fuel supply amount at a fixed level for a predetermined
time following correction of the fuel supply amount. This enables
an accurate temperature measurement which excludes the effects of
changes to the fuel supply amount by correction.
When the degradation processing described above is completed, the
degradation determining circuit 110a ends the degradation
determining mode operation, and the control section 110 resumes
normal operation responsive to the required generation amount (FIG.
9, time t2).
Next, referring to FIGS. 13 and 14, we discuss selection of the
correction mode using the mode selection device 110c. FIGS. 13 and
14 are timing charts schematically depicting the operational
history of the solid oxide fuel cell 1 over approximately 1 year;
starting from the top portion, what is shown is the power consumed
by a user (shown by a dotted line), the power generated by the
solid oxide fuel cell 1 (shown by a solid line), the fuel supply
amount, and the fuel cell unit temperature. Note that there is a
tendency for the power consumption in a typical household to be
large during the day and small at night, therefore the timing
charts shown in FIGS. 13 and 14 extract only the operating history
from 6:00 AM to 12:00 midnight, which is the primary time period
for power consumption, and the operating state recording device
110d records approximately 1 year's worth of this type of operating
history.
At times t100-t103 in FIG. 13, the power consumed by the user
constantly exceeds the rated output power of the solid oxide fuel
cell 1, which is its maximum output power, therefore an amount of
fuel suited to the rated power is being constantly supplied to the
fuel cell module 2, and the solid oxide fuel cell 1 is constantly
generating its rated output power. Note that the portion of the
consumed power not supplied by the rated output power is supplied
from the electrical grid. Also, when the fuel cell module 2
degrades due to long usage, the output voltage of the fuel cell
module 2 declines relative to the same fuel supply amount, and the
temperature of the fuel cell units 16 rises. To output the rated
power in a state in which the fuel cell module 2 output power
voltage has declined requires an increase in the current extracted
from the fuel cell module 2. However, if the current extracted from
the fuel cell module 2 becomes too large, the burden on the fuel
cell units 16 becomes great, leading to faster degradation of the
cells. For this reason, in the present embodiment the current
extracted from the fuel cell module 2 is restricted to a
predetermined current or less. As a result of this current value
restriction, the output power falls at times t101-t102 in FIG. 13,
even though the fuel supply amount is constant.
Next, at time t103 in FIG. 13, the above-described degradation
determination is executed. At time t103, the temperature T1 of the
fuel cell units 16 is 30.degree. C. or more higher than the
reference temperature T0 of the fuel cell units 16 at initial use,
therefore the degradation determining circuit 110a determines that
the fuel cell module 2 has degraded (step S6 in FIG. 12).
The operating state recording device 110d records operating history
during the daytime for the solid oxide fuel cell 1 over the past 1
year, and the mode selection device 110c automatically selects the
increasing correction mode or the decreasing correction mode based
on past operating states recorded in the operating state recording
device 110d. In the example shown in FIG. 13, power consumption is
constantly higher than the rated output power, and the fuel cell
module 2 is constantly outputting its rated output power, therefore
the mode selection device 110c selects the increasing correction
mode, which causes the fuel correction circuit 110b to make an
increasing correction to the fuel supply amount. By the increasing
correction, the control section 110 changes the curve for
determining the fuel supply amount from curve F0 to curve F1 in
FIG. 10, and the fuel supply amount is increased (time t103 in FIG.
13). As a result of the increase in the fuel supply amount, the
power output by the fuel cell module 2 is restored to the initial
rated output power (times t103-t104 in FIG. 13). The temperature of
the fuel cell units 16 after a predetermined time has elapsed from
the increasing correction is stored as reference temperature T0 in
the degradation determining circuit 110a and used in the next
degradation determination.
As shown in the FIG. 13 example, in cases where the time during
which the rated output power is being produced was long within a
predetermined period in the past, an increasing correction is
selected to maintain the initial rated output power when it is
determined that the fuel cell module 2 has degraded. This makes it
possible to reduce the amount of power received from the electrical
grid and thereby cut the cost of power purchases from the grid.
On the other hand, in the example shown in FIG. 14, the time in the
operating history recorded in the operating state recording device
110d during which the user's power consumption was below the rated
power of the solid oxide fuel cell 1 (times t201-t202 in FIG. 14)
is longer than the time during which that consumption was higher
(times t200-t201 and t202-t205 in FIG. 14). Also, in the FIG. 14
example, the fuel cell module 2 degrades due to long use at times
t203-t204, and the output power for the same fuel supply amount
declines as the temperature of the fuel cell units 16 rises. Note
that the decline in output power at times t203-204 is also the
result of the restriction on the current value extracted from the
fuel cell module 2.
Next, at time t205 in FIG. 14, a degradation determination is
executed. At time t204, the temperature T1 of the fuel cell units
16 is 30.degree. C. or more higher than the reference temperature
T0 of the fuel cell units 16 at initial use, therefore the
degradation determining circuit 110a determines that the fuel cell
module 2 has degraded (step S6 in FIG. 12).
As shown in the FIG. 14 example, when, as an operating state, the
time within a predetermined past period during which the solid
oxide fuel cell 1 was operated at less than its rated output was
longer than the time during which it was operated at or above its
rated output, the mode selection device 110c selects a decreasing
correction mode if the degradation determining circuit 110a
determines that the fuel cell module 2 has degraded. This causes
the fuel correction circuit 110b to execute a correction to
decrease the fuel supply amount. By the decreasing correction the
control section 110 changes the curve for determining the fuel
supply amount from curve F0 to curve F-1 in FIG. 10, and the fuel
supply amount is decreased (time t205 in FIG. 14). The reduction in
the fuel supply amount causes the fuel cell module 2 output power
to be reduced, but the temperature of the fuel cell units 16 also
declines (times t205-t207 in FIG. 14). The temperature of the fuel
cell units 16 after a predetermined time has elapsed from the
decreasing correction (the temperature at times t206-t208 in FIG.
14) is stored as reference temperature T0 in the degradation
determining circuit 110a and used in the next degradation
determination.
As shown in the FIG. 14 example, when the time in past operating
states during which operation was conducted at less than the rated
output power was long, a decreasing correction is selected. This
results in an increase to the amount of power received from the
electrical grid when the power consumed by the user is large, but
because that time period is short, the cost of power purchases from
the electrical grid does not increase very much. On the other hand,
the temperature of the fuel cell units 16 decreases due to the
decreasing correction of the fuel supply amount, therefore
degradation of the fuel cell module 2 can be restrained.
As explained above, when it is determined for the first time by the
degradation determining circuit 110a that the fuel cell module 2
has degraded, the mode selection device 110c selects either the
decreasing correction mode or the increasing correction mode. When
degradation of the fuel cell module 2 is determined for the first
time, and the decreasing correction mode is selected, the curve
which determines the fuel supply amount is changed from the curve
F0 in FIG. 10 to the curve F-1, in which the fuel supply amount is
reduced by 10% relative to curve F0. After this fuel supply
correction, the fuel supply amount is reduced relative to the same
required generation amount, and the power actually output relative
to required generation amount is reduced. After fuel supply
correction, the actual output power of the fuel cell module 2
relative to the required generation amount of 700 W, which is the
initial rated output power, is treated as a reduced new rated
output power. By reducing the fuel supply amount, excessive rises
in the fuel cell module 2 temperature are prevented. A sudden
change to the amount of fuel supplied to a fuel cell module 2 can
lead to further degradation, therefore the rate of change in the
fuel supply amount is made smaller.
Furthermore, when, in the decreasing correction mode, degradation
of the fuel cell module 2 advances and the fuel cell module 2 is
determined to have further degraded, the fuel supply amount is
changed from curve F-1 to curve F-2, and when there is still
another decreasing correction, it is changed from curve F-2 to
curve F-3. The curve F-2 represents a 20% fuel supply amount
reduction relative to curve F0, and the curve F-3 a 30% reduction
relative to curve F0. Excessive burden on the fuel cell units 16 in
which degradation is progressing can in this way be prevented. The
fuel supply amount gain is also changed from line F11 to line F12
on the second execution of a decreasing correction, and from line
F12 to line F13 on the third execution of a decreasing
correction.
On the other hand, when degradation of the fuel cell module 2 is
determined for the first time, and the increasing correction mode
is selected, the curve which determines the fuel supply amount is
changed from the curve F0 to the curve F1 in FIG. 10, in which the
fuel supply amount is increased by 10% relative to curve F0. After
this fuel supply correction, the fuel supply amount relative to the
same required generation amount is increased, and the initial rated
output power of 700 W is maintained even if the fuel cell module 2
has degraded. By increasing the fuel supply amount, a power equal
to that at the initial usage period of the fuel cell module 2 can
be extracted.
Furthermore, when degradation of the fuel cell module 2 advances in
the increasing correction mode and the fuel cell module 2 is
determined to have further degraded, the fuel supply amount is
changed from curve F1 to curve F2; when there is still another
increasing correction, it is changed from curve F2 to curve F3. The
fuel supply amount in curve F2 is decreased 18% relative to curve
F0, and 23% in curve F3 relative to curve F0. Thus by decreasing
the amount of increase to the fuel as degradation progresses, the
rise in temperature and excessive burden on the fuel cell units 16
in which degradation is progressing can be prevented. And as in the
decreasing correction mode, the fuel supply amount gain is changed
from line F11 to line F12 on the second execution of a decreasing
correction, and from line F12 to line F13 on the third execution of
a decreasing correction.
Thus in the present embodiment the amount of change to the fuel
supply amount is a pre-set fixed value, both when executing a
decreasing correction and when executing an increasing correction.
Corrections greatly in error can therefore be prevented from
occurring, unlike, for example, when the fuel supply amount
correction amount is calculated based on the temperature rise in
the fuel cell units 16, or based on the amount of reduction in
output power. In other words, the temperature or output power of
the fuel cell units 16 is affected by various factors which change
their values, so calculating the amount of correction based on
these values results in the execution of anomalous corrections when
an anomalous temperature or output power is measured due to some
factor.
Next, referring to FIGS. 15 through 18, we discuss details of a
fuel correction by the fuel correction circuit 110b. FIG. 15 is a
timing chart showing an example of the action of the solid oxide
fuel cell 1 when the decreasing correction mode is selected by the
mode selection device 110c; FIG. 16 is a flow chart of fuel
correction processing in the decreasing correction mode. FIG. 17 is
a timing chart showing an example of the action of the solid oxide
fuel cell 1 when the increasing correction mode is selected; FIG.
18 is a flow chart of fuel correction processing in the increasing
correction mode.
Note that FIGS. 15 and 17 are timing charts in which the horizontal
axis shows time, and the vertical axis shows output power, fuel
supply amount, and fuel cell unit temperature, but these are
schematically showing the fuel cell operating states over a much
longer time period than the timing chart shown in FIG. 9. Also,
because the timing charts are simplified, the solid oxide fuel cell
1 is depicted as always being operated at rated output power. The
flow charts shown in FIGS. 16 and 18 are called as subroutines by
step S7 in the flow chart shown in FIG. 12; when the decreasing
correction mode is selected, the FIG. 16 flow chart is called, and
when the increasing correction mode is selected, the FIG. 18 flow
chart is called.
Initial use of the solid oxide fuel cell 1 is begun at time t300 in
FIG. 15. At the time of initial operation, rated output power is
obtained by operating the solid oxide fuel cell 1 at a specified
fuel supply amount; the temperature at this point is stored in the
degradation determining circuit 110a as the initial reference
temperature T0 for fuel cell units 16. Degradation of the fuel cell
module 2 begins as the solid oxide fuel cell 1 usage time extends,
reducing the output voltage of the fuel cell module 2 relative to
the same amount of fuel supplied. Output power declines together
with the decline in this output voltage as a result of the
operation of the output current restriction, and the temperature of
the fuel cell units 16 also rises (times t301-t302 in FIG. 15).
Next, at time t303, a degradation determination is carried out and
the flow chart shown in FIG. 12 is executed. At time t303, the
temperature of the fuel cell unit 16 during rated output power
operation has risen 30.degree. C. or more above the reference
temperature T0 (the temperature at time t300), therefore it is
determined that a fuel cell module 2 has degraded, and processing
shifts from step S6 to step S7 in FIG. 12. In the example shown in
FIG. 15, the decreasing correction mode is selected by the mode
selection device 110c. Because the decreasing correction mode was
selected, the subroutine shown in FIG. 16 is called by step S7 in
FIG. 12.
In step S101 of FIG. 16, the value of the switching flag FL1 is
determined. In the solid oxide fuel cell 1 initial state, the
switching flag FL1 is set to 0, therefore processing moves to step
S102. In step S102, a determination is made of the temperature T1
of the fuel cell unit 16 at time t303. In other words, when the
required generation amount is the rated power, the temperature T1
of the fuel cell units 16 is less than the correction switching
temperature Tmax1 in the decreasing correction mode, which is a
predetermined correction switching condition, the system advances
to step S103; if the temperature T1 is equal to or greater than the
correction switching temperature Tmax1, the system advances to step
S106. Note that in the present embodiment, the correction switching
temperature in the decreasing correction mode is set to
Tmax1=800.degree. C.
In step S103, the value of the decreasing correction iteration
counter is determined. The decreasing correction iteration counter
is a counter for totaling the number of iterations of decreasing
corrections to the fuel supply amount after the initial start of
use. If the number of decreasing corrections is less than 3, the
system advances to step S104; if 3 or greater, it advances to step
S106.
In step S104, the fuel supply amount is corrected to decrease (time
t303 in FIG. 15) so that degradation of the degraded fuel cell
module 2 does not advance, and the decreasing correction iteration
counter is increased by 1. At this point, if this is the first
decreasing correction, the curve determining the fuel supply amount
is changed from curve F0 to curve F-1 in FIG. 10, and the
decreasing correction iteration counter value is changed from a 0
to a 1. The temperature when a predetermined time has elapsed after
a decreasing correction to the fuel supply amount (the temperature
at times t304-t305 in FIG. 15) is updated and stored as a new
reference temperature T0 (step S8 in FIG. 12). As a result of this
decreasing correction to the fuel supply amount, the rated output
power actually output by the solid oxide fuel cell 1 declines, as
does the temperature of the fuel cell units 16 (times t303-t305 in
FIG. 15).
When a further solid oxide fuel cell 1 usage period has elapsed,
degradation of the fuel cell module 2 advances further, and output
power relative to fuel supply amount declines, while the
temperature of the fuel cell unit 16 also rises (times t305-t306 in
FIG. 15). Next, at time t307, a degradation determination is
performed. At time t307, the temperature of the fuel cell unit 16
during rated output power operation has risen 30.degree. C. or more
above the updated reference temperature T0 (the temperature at
times t304-t305), therefore a degradation is determined to have
occurred, and processing shifts from step S6 to step S7 in the flow
chart shown in FIG. 12.
Here, at the time t303 where it was first determined that a
degradation of the fuel cell module 2 had occurred, the decreasing
correction mode is selected, therefore at step S7 in FIG. 12 the
FIG. 16 flow chart is called, and steps S101, S102, S103, and S104
are executed in sequence. If this is second decreasing correction,
the curve determining the fuel supply amount is changed from curve
F-1 to curve F-2 in FIG. 10; the decreasing correction iteration
counter value is changed from a 1 to a 2, and the fuel supply
amount is further corrected downward (time t307 in FIG. 15). As a
result of this decreasing correction to the fuel supply amount, the
output power actually output by the solid oxide fuel cell 1
declines, as does the temperature of the fuel cell units 16 (times
t307-t308 in FIG. 15).
When degradation of the fuel cell module 2 further advances, the
output power of the solid oxide fuel cell 1 declines, and the
temperature of the fuel cell units 16 increases (times t309-t310 in
FIG. 15). Next, at time t311, a degradation determination is
performed.
At time t311, the temperature of the fuel cell units 16 during
rated output power operation has risen 30.degree. C. or more above
the updated reference temperature T0 (the temperature at times
t308-t309), therefore processing shifts from step S6 to step S7 in
the flow chart shown in FIG. 12. As described above, the decreasing
correction mode is selected, therefore at step S7 the FIG. 16 flow
chart is called, and steps S101, and S102 are executed in sequence.
In step S102, the temperature T1 of the fuel cell units 16 at time
t311 exceeds the correction switching temperature Tmax1 in the
decreasing correction mode, therefore the system moves to step
S106.
In step S106, the switching flag FL1 value is changed from a 0 to a
1. The switching flag FL1 is a flag indicating whether, in the
decreasing correction mode, the fuel correction circuit 110b is
executing a correction to reduce the rated output power so that the
fuel supply amount is reduced. When the value of the switching flag
FL1 is a 0, a decreasing correction is applied to the fuel supply
amount; when the switching flag FL1 value is switched to a 1,
thereafter the fuel correction circuit 110b causes the fuel supply
amount to increase, and executes a correction in the direction of
maintaining the diminishing rated output power (step S107 in FIG.
16). Thus when the decreasing correction mode is selected, the fuel
correction circuit 110b first executes a correction to reduce the
fuel supply amount, and when degradation of the fuel cell module 2
has progressed to some degree and the correction switching
conditions are satisfied, i.e., when the correction switching
temperature Tmax1 is exceeded, the fuel supply amount is increased
and a correction is executed so that the rated output power does
not decline any further.
Note that in the timing chart shown in FIG. 15, the value of the
switching flag FL1 is changed from 0 to 1 due to the fact that the
temperature of the fuel cell units 16 during rated output operation
exceeds the correction switching temperature Tmax1, but the
switching flag FL1 value is changed from 0 to 1 even when a
decreasing correction of the fuel supply amount has been performed
3 times in the past (step S103 in FIG. 16); thereafter corrections
are executed to increase the fuel supply amount.
Next, in step S107, a correction to increase the fuel supply amount
is executed so as to maintain the rated output power being
diminished (the output power at times t308-t309 in FIG. 15).
Specifically, the fuel correction circuit 110b increases the fuel
supply amount by a pre-set fixed value only (time t311 in FIG. 15).
This increasing correction of the fuel supply amount causes output
power to recover, while at the same time the temperature of the
fuel cell units 16 increases (times t311-t312 in FIG. 15).
Furthermore, in step S108 a determination is made of the output
power value (the power at times t312-t313 in FIG. 15) after an
increasing correction of the fuel supply amount is performed. When
the post-increasing correction output power is larger than a
predetermined minimum power Wmin, the system advances to step S109,
and one iteration of the FIG. 16 flow chart is completed. If the
output power is the predetermined minimum power Wmin or less, the
system advances to step S110.
When a further usage period elapses, degradation of the fuel cell
module 2 advances further, and output power relative to fuel supply
amount declines, while the temperature of the fuel cell unit 16
also rises (times t313-t314 in FIG. 15).
Next, at time t314, a degradation determination is performed; if it
is determined that further degradation of the fuel cell module 2
has occurred, steps S101 and S107 in the FIG. 16 flow chart are
executed in sequence. At step S107, the fuel correction circuit
110b further increases the fuel supply amount by a pre-set fixed
value only (time t314 in FIG. 15). This increasing correction of
the fuel supply amount causes output power to recover, while at the
same time the temperature of the fuel cell units 16 increases
(times t314-t315 in FIG. 15). The recovered output power (the
output power at times t315-t316 in FIG. 15) is larger than the
minimum power Wmin, therefore the system advances to step S109, and
one iteration of the FIG. 16 flow chart processing is
completed.
When a further usage period elapses, degradation of the fuel cell
module 2 advances further, and output power relative to fuel supply
amount declines, while the temperature of the fuel cell unit 16
also rises (times t316-t317 in FIG. 15).
Next, at time t317, a degradation determination is performed; if it
is determined that further degradation of the fuel cell module 2
has occurred, steps S101 and S107 in the FIG. 16 flow chart are
executed in sequence. At step S107, the fuel correction circuit
110b further increases the fuel supply amount (time t317 in FIG.
15). However, because degradation of the fuel cell module 2 is
advancing, there is no recovery of the output power, and only the
temperature of the fuel cell units 16 rises (times t317-t318 in
FIG. 15).
Next, in step S108, the post-increasing correction output power
(the output power at time t318 in FIG. 15) is compared to the
minimum power Wmin. At time t318, the output power is at or below
the minimum power Wmin, so the system advances to step S110. In
step S110, the control section 110 sends a signal to the warning
device 116 to inform users that the solid oxide fuel cell 1 has
reached its product life, and stops operation of the fuel cell
module 2.
Next, referring to FIGS. 17 and 18, we discuss the action of the
solid oxide fuel cell 1 in this embodiment when the increasing
correction mode has been selected. Note that the flow chart shown
in FIG. 18 is essentially the same as the flow chart shown in FIG.
16; it differs from FIG. 16 with respect to the points that in step
S202 of FIG. 18 the temperature T1 of the fuel cell units 16 is
compared to the correction switching temperature Tmax2 in the
increasing correction mode, that in step S204 the fuel supply
amount is corrected to increase, and that in step S208 the fuel
supply amount is corrected to decrease. Note that in the present
embodiment, the correction switching temperature in the increasing
correction mode is set to Tmax2=900.degree. C.
At time t400 in FIG. 17, initial use of the solid oxide fuel cell 1
is started. At time t401, a degradation of the fuel cell module 2
is first determined, and the increasing correction mode is selected
using the mode selection device 110c. The FIG. 18 flow chart is
thus called by step S7 in FIG. 12. In the FIG. 18 flow chart, steps
S201, S202, S203, and S204 are executed in sequence, and an
increasing correction of the fuel supply amount is executed by the
fuel correction circuit 110b (step S204 in FIG. 18). The curve
determining the fuel supply amount is thus changed from curve F0 to
curve F1 in FIG. 10, and the increasing correction iteration
counter value is changed from a 0 to a 1.
At time t402 in FIG. 17, where degradation has progressed further,
the degradation determining circuit 110a makes a second
determination of fuel cell module 2 degradation, and a second
increasing correction to the fuel supply amount is executed by the
fuel correction circuit 110b. The curve determining the fuel supply
amount is thus changed from curve F1 to curve F2 in FIG. 10. At
time t403 a third determination of fuel cell module 2 degradation
is made, and a third increasing correction of the fuel supply
amount is executed. The curve determining the fuel supply amount is
thus changed from curve F2 to curve F3 in FIG. 10.
Next, at time 1404 in FIG. 17, a fourth determination of fuel cell
module 2 degradation is made, and the FIG. 18 flow chart is called
by step S7 in FIG. 12. At time t404, increasing corrections have
been made 3 times in the past, therefore in the FIG. 18 flow chart
steps S201, S202, S203, and S206 are executed in sequence, and the
value of switching flag FL2 is changed from 0 to 1. Next, in step
S207, a decreasing correction of the fuel supply amount is executed
by the fuel correction circuit 110b (time t404 in FIG. 17). Because
the value of switching flag FL2 is changed to a 1, a decreasing
correction of the fuel supply amount is made when it is determined
by the degradation determining circuit 110a that the fuel cell
module 2 has degraded. As in the case of the decreasing correction
mode, this degradation determination and decreasing correction of
the fuel supply amount is repeated until the post-correction output
power falls below the minimum power Wmin.
In the solid oxide fuel cell 1 of this embodiment of the invention,
the mode selection device 110c selects the increasing correction
mode (time t103 in FIG. 13) or the decreasing correction mode (time
t205 in FIG. 14), therefore an appropriate mode can be selected in
accordance with fuel cell usage conditions, so that product life
can be extended while a practical output power is maintained.
In the solid oxide fuel cell 1 of this embodiment of the invention,
the mode selection device 110c selects the correction mode based on
past operating states stored in the operating state recording
device 110d, therefore an appropriate correction mode can be
automatically selected.
Moreover, in the solid oxide fuel cell 1 of this embodiment of the
invention when, as a fuel cell module 2 past operating state, the
time during which the rated output power was being output is
longer, the increasing correction mode is selected (FIG. 13) and
the rated output voltage is maintained even after the fuel cell
module 2 has degraded, therefore grid power utilization charges can
be saved. On the other hand, when the time during which the rated
output power is output is shorter, the decreasing correction mode
is selected (FIG. 14), and rated output voltage declines, therefore
the amount of fuel consumption by the fuel cell module 2, whose
efficiency has declined due to degradation, can be restrained, and
energy can be conserved.
We have explained preferred embodiments of the present invention
above, but various changes may be added to the above-described
embodiments. In the embodiment described above, the mode selection
device 110c was selecting the increasing correction mode or the
decreasing correction mode based on the entire operating history,
until from the point of the first determination of fuel cell module
2 degradation, but as a variation the correction mode could also be
selected based on recent operating history.
In the timing chart example shown in FIG. 19, initial use is
started at time t500, and power equal to or greater than the rated
power of the solid oxide fuel cell 1 is consumed until around time
t501, when 10 years have elapsed; thereafter power consumption
diminishes due to changes in user family composition and the like.
If the degradation determining circuit 110a here determines that
the fuel cell module 2 has degraded during the period from time
t501 to time t505 one year later, then in the above-described
embodiment the period during which consumed power is equal to or
greater than rated power is shorter than the period during which
consumed power is less than rated power, therefore the increasing
correction mode is selected by the mode selection device 110c. In
this variation, the increasing correction mode is selected based on
the operating state during the most recent one year from times t501
to t505 in FIG. 19, therefore the decreasing correction mode is
selected by the mode selection device 110c. A decreasing correction
is thus executed at time t505 in FIG. 19, and the rated power is
reduced.
In this variation, the correction mode is selected based on the
operating state in a predetermined recent period, therefore the
appropriate post-degradation determination correction mode can be
selected if the user's power consumption trends have changed
subsequent to initial start of use.
In the above-described embodiment the correction mode was selected
automatically by the mode selection device 110c built into the
control section, but as a variation, the present invention could be
constituted by providing a mode selecting operating device 112 for
selecting the increasing correction mode or decreasing correction
mode so that the correction mode could be selected by manipulating
the operating device 112.
In this case, the mode selecting operating device 112 could be
constituted to be set as desired at the time the solid oxide fuel
cell is shipped from the factory. In a variation thus constituted,
an appropriate correction mode could be pre-selected in accordance
with the location at which the solid oxide fuel cell is to be
installed.
Alternatively, the mode selecting operating device 112 could be
constituted to be manipulable by users when a fuel cell module is
first determined to have degraded. In a variation thus constituted,
an appropriate correction mode could be pre-selected according to
future electrical usage conditions anticipated by the user.
In the above-described embodiment the selection of a correction
mode by the mode selection device when the fuel cell module was
first determined to have degraded was carried out only once, but as
a variation the present invention could also be constituted to
carry out the correction mode selection multiple times. For
example, the present invention could be constituted so that a
correction mode selection was performed each time a predetermined
number of fuel cell module degradation determinations occurred.
In the variation thus constituted, an appropriate correction mode
could be reselected in cases where a user's power demand trends
changed after the correction mode had already been selected
once.
EXPLANATION OF REFERENCE NUMERALS
1: Solid oxide fuel cell 2: Fuel cell module 4: Auxiliary unit 8:
Sealed space 10: Electrical generating chamber 12: Fuel cell
assembly 14: Fuel cell stack 16: fuel cell units (solid oxide fuel
cells) 18: Combustion chamber 20: Reformer 22: Heat exchanger for
air 24: Water supply source 26: Pure water tank 28: Water flow rate
regulator unit (water supply device; water supply means) 30: Fuel
supply source 38: Fuel flow rate regulator unit (fuel supply
device, fuel supply means) 40: Air supply source 44: Reforming air
flow rate regulator unit 45: Generating air flow rate regulator
unit (oxidant gas supply device; oxidant gas supply means) 46:
First heater 48: Second heater 50: Hot water production device 52:
Control box 54: Inverter 83: Ignition device 84: Fuel cells 110:
Control section (controller, control means) 110a: Degradation
Determining Circuit (degradation determining means) 110b: Fuel
correction circuit (fuel correction means) 110c: mode selection
device (mode selection means) 110d: operating state recording
device (operating state recording means) 112: Operating device 114:
Display device 116: Warning device 126: Power state detection
sensor 142: Generating chamber temperature sensor (temperature
detection means) 150: Outside air temperature sensor
* * * * *